Parts of the above mentioned type, which contain fluid channels, require through-going orifices so that the fluid can be supplied and carried away. Through-going orifices can be worked into the part using mechanical processes after the injection molding process. However, it is much more efficient to produce the through-going orifices at the time of injection molding. For this purpose pins (hereinafter referred to as ‘piercing punches’) are inserted into the two tool halves at the sites where the part is to comprise a through-going orifice and as the two tool halves are closed two mutually opposite piercing punches always push against each other (hereinafter referred to as ‘squeezing’). During the subsequent process of injecting the material melt, for example, the synthetic material melt, through-going orifices are formed where the piercing punches are located.
The requirements in micro-injection molding processes for the piercing punches to fit accurately into the tools, in particular on the microstructured tool halves, are much higher than in conventional injection molding processes, the reason being, that in order to form microstructures of identical shapes, the material melt must have an extremely low viscosity, but this increases the risk that the material melt penetrates between the piercing punch and the tool into where they fit together, where it forms a flash. This flash can lead to the connection between the through-going orifice and the microchannel becoming partially or completely blocked, thus rendering the microchannel and the entire part unusable. A further disadvantage is that the through-going orifices in the case of microstructured parts must also be small, on the one hand so that they do not occupy unnecessary space and on the other hand so that they receive extremely small volumes of fluid. The manufacturing costs are correspondingly higher. At this moment in time fitting orifices for piercing punches with a diameter of less than 1 millimeter can currently only be produced with the required precision at great effort and cost.